Electron discharge device



Dec. 3, 1935. F, H LSTE 2,b23,272

ELECTRON DI SCI-IARGE DEVICE Filed July 13, 1935 INVENTOR FRITZ HULSTER ATTORNEY Patented Dec. 3, 1935 UNITED STATES PATENT OFFICE ELECTRON DISCHARGE DEVICE Germany Application July 13, 1935, Serial No. 31,142 In Germany July 5, 1934 5 Claims.

My invention relates to electron discharge devices for use at high frequencies of the type referred to as a magnetron, and more particularly to means for insuring stable operation of such devices.

In the operation of magnetron tubes for producing and receiving very short waves there is often a pronounced overheating of the cathode causing an accelerated increase of the anode current and a rapid destruction of the tube. It was previously thought that this phenomenon was due to the anode attaining prohibitively high temperatures, and heating the cathode by heat radiation. Attempts have therefore been made to eliminate this difiiculty by artificially cooling the anode, for example by means of water circulation. However, this back heating effect of the cathode was not avoided by this arrangement. It is therefore believed that this phenomenon of heating is caused by ions, or such electrons as derive energy from the alternating electric field so that they are subjected to an acceleration in improper phase relationship during operation of the tube.

It is therefore the principal object of my invention to provide an improved means for insuring stable operation of an electron discharge device of the magnetron type.

In accordance with the invention the prohibitive increase of the plate current can be effectively suppressed by inserting current limiting devices in the anode current circuit. Overload relays disconnecting the plate voltage source in case of excess of a permissible maximum current are unsuitable for this purpose, since they are incapable of assuring a stabilization of operation. But the result is obtained by using a device inserted in the plate circuit and having a saturation characteristic. Such devices are available in the form of electron discharge tubes whose current-voltage characteristic is characterized by a saturation current which remains substantially constant after a predetermined voltage is reached. Electron discharge tube having a metal cathode, for example tungsten wire, have this characteristic: so-called space charge grid tubes i. e. discharge tubes in which the cathode is enclosed by a positively biased grid, whereby the cathode of the space charge grid tube may be a high emission cathode, oxide coated for example, without defined saturation properties may also be used for this purpose. Where such a device is inserted in the plate circuit, the plate current cannot exceed the value of the saturation current of the additional discharge path of the electron discharge device even if the cathode of the megnetron does assume a higher temperature due to back heating, or radiation from the anode.

This arrangement stabilizes operation of the magnetron. The voltage drop through the current limiting device can be made negligibly small in comparison with the direct plate potential of the magnetron especially if the limiting device is provided with means for eliminating the space charge such as a space charge grid or a gas filling.

It may further be mentioned that the current limiting device makes it possible to provide the magnetron tube with a cathode having no defined saturation characteristic, for example an oxide coated cathode. The use of high power cathodes is very desirable in view of the decrease in the required amount of heating energy, on the other hand; the operation of the magnetron presupposes a cathode having a saturation characteristic (constant emitting current independent of the plate potential). The application of this invention insures both advantages.

The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claims, but the invention itself will best be understood by reference to the following description taken in connection with the accompanying drawing in which the single figure of the drawing is a schematic circuit diagram for use with a magnetron tube and embodying my invention.

In the drawing, the magnetron tube has an envelope l containing a thermionic cathode 2 and two semi-cylindrical anode segments 3, 4. An electro-magnetic coil 4' furnishes the magnetic field. The anodes operating in push-pull have a parallel conductor system 5, 6 connected thereto which can be tuned to the frequency of the oscillations to be produced or to be received by means of a slidable bridge 1. The heating voltage is supplied by a source VH and the plate potential by a source VA through a choke II. The plate current is supplied across an electron discharge While I have indicated the preferred embodiments of my invention of which I am now aware and have also indicated only one specific application for which my invention may be employed, it will be apparent that my invention is by no means limited to the exact forms illustrated or the use indicated, but that many variations may be made in the particular structure used and the purpose for which it is employed without departing from the scope of my invention as set forth in the appended claims.

What I claim as new is:

1. A magnetron having a thermionic cathode and a plurality of anodes, an oscillating circuit connected to said anodes, a source of voltage for said anodes and means connected between said source of voltage and said anodes for limiting the anode current during operation to a predetermined maximum.

2. A magnetron having a thermionic cathode and a plurality of anodes, an oscillating circuit connected to said anodes, a source of voltage for said anodes and an electron discharge device having a current saturation characteristic connected between the source of voltage and said anodes for limiting the anode current during operation of the magnetron to a predetermined maximum.

3. A magnetron having a straight thermionic filament cathode and a plurality of parallel anodes, an oscillating circuit connected to said anodes, a source of voltage for said anodes, an electron discharge device connected between said anodes and said source of voltage supply and having a thermionic cathode, an anode and a grid, and means for maintaining said grid at a positive potential with respect to the cathode, said electron discharge device having a current saturation characteristic whereby the current to said anodes during operation of the magnetron is limited to a predetermined maximum.

4. A magnetron having a straight thermionic cathode and a plurality of parallel anodes, an oscillating circuit connected to said anodes, a source of voltage for said anodes, an electron discharge device connected between said anodes and said source of voltage supply and having a thermionic cathode, an anode and a grid, a source of heating current for the cathode of said electron discharge device, a means for maintaining said grid at a positive potential with respect to the cathode, said electron discharge device having a current saturation characteristic and limiting the current to said anodes during operation of the magnetron to a predetermined maximum, and means for varying the heating current to the cathode of said electron discharge device for varying the predetermined maximum current flowing to the magnetron anodes.

5. A magnetron having a straight thermionic cathode and a plurality of parallel anodes, an oscillating circuit connected to said anodes, a source of voltage for said anodes, an electron discharge device connected between said source of voltage and said anodes and having a thermionic cathode, an anode and a grid, and means for applying a variable positive potential to said grid whereby the maximum saturation current through said electron discharge device may be varied to control the maximum current to the anodes of said magnetron.

FRITZ HUL" STER. 

